Since the 1700's, shoe inventions have dealt primarily with ways to make shoes, rather than with ways to make them fit, the latter having been considered the proper province of the manufacturer and his suppliers.
We find ourselves more than two centuries later, with excellent machinery making vast quantities of shoes, most of which do not fit nearly as well as they should.
For a shoe to fit properly, it should have a transverse girth which is substantially the same as the girth of the wearer's foot, girth being the transverse circumference around the foot, typically measured at the ball waist and instep of the foot.
However, foot girth dimensions vary over a range of up to two inches for each length size while most popular price shoes now come in only one width per length, to allow marketing of the maximum number of styles with the minimum inventory, for end users who apparently value style and price over the homelier virtues of fit and comfort.
Furthermore, research has shown that a foot usually varies in girth up to two standard widths daily with even greater changes under a variety of physiological conditions causing fluid and/or tissue buildup in the foot.
The prior art has dealt mainly with visible means of girth adjustment such as laces, adjustment straps, and the like, most of which usually do not provide adjustment at the ball of the foot; nor are they useful in the many popular non-adjustable shoe styles, such as boots, slip-ons, loafers, women's pumps, flats, and so forth.
The prior art has also neglected the children's field, where self-adjusting girth would allow a shoe to better fit the growing foot, as well as facilitate the wearing of new slip-on styles that the child would not have to tie or otherwise adjust.
Adjustable girth footwear is not new, as shoes having this capability are disclosed, for example, in my U.S. Pat. Nos. 3,404,468; 3,541,708 and 3,686,777. These prior shoes have a non-stretchable upper with longitudinally extending lower edge margins at least in the forepart of the shoe turned in toward one another and being free of the direct connection to the sole element.
In one version, shown in FIGS. 1 to 8 of the first-mentioned patent, at least one of those edge margins in the forepart of the shoe is connected by way of stretchable elastic sheet material extending under the wearer's foot to the middle of the sole element or to the other edge margin; in other shoe versions depicted in FIGS. 9 to 13 of that same patent, those edge margins are connected via the elastic material to the edges of the sole element. All of those shoe constructions provide automatic adjustment of the shoe girth to suit the wearer's foot.
The latter two patents above disclose, in lieu of such elastic sheet material, mechanisms for adjusting the spacing of those shoe upper margins so that girth adjustment can be accomplished manually. While those prior shoe constructions have contributed appreciably to the art, they have certain drawbacks which have tended to inhibit their adoption and use. More particularly, in the described first version of that prior shoe, pebbles, dirt and water tend to infiltrate between the upper and the sole element at each lengthwise segment of the shoe where there is no direct connection between the shoe upper and the sole element. Also, the shoe upper tends to pull away from the sole element along each such segment thereby spoiling the appearance of the shoe. In other versions, the elastic sheet material, tends to lose its elasticity due to exposure to sun, ozone, ageing and wear so that the girth adjustment capability of those shoes tends to become degraded over time. Also the elastic material, being a relatively thin sheet of stretch nylon, spandex or the like located right at the sole of the shoe soils easily and is prone to being cut, worn and punctured by contact with curbs, stones and other objects thereby allowing water to penetrate into the shoe. Still further, that exterior stretch material is quite expensive so that shoes of this type would tend not to be economically competitive.
Another technique for adjusting the girth of a shoe essentially by adjusting the elevation of the foot within the shoe is disclosed in U.S. Pat. No. 3,442,031. In this arrangement, a plural-layer auxiliary sole is inserted into the shoe between the insole and sock lining thereby reducing the amount of upper material that extends above the surface that supports the foot. Each of the layers is of such a thickness as to change the girth of the shoe forepart by one standard width. Thus, by removing one layer more upper material is available above that support surface to accommodate a foot one size wider. If a second layer is removed, still more upper material extends above the support surface so that a still wider foot can be accommodated in the shoe. This prior shoe construction is disadvantageous because a person's feet often have different girths or widths. Therefore, adjusting shoe girth in this fashion by elevating the foot within the shoe means that a person's feet may be supported at different heights. This is very undesirable because it has been found that a foot height difference of as little as three sixteenths of an inch is sufficient to cause permanent injury to a person's back and legs. This could tend to provoke heavy liability litigation which the industry as a whole prefers to avoid.
In sum, in all of my prior adjustable girth shoe constructions, the critical lack of a continuous, firm, nonstretchable, nonelastic edge connection between the shoe upper and the sole element all around the shoe has contributed to the lack of acceptance of such constructions. On the other hand, the solution described in the aforementioned U.S. Pat. No. 3,442,031 fails to maintain the designed tread of the last and the shoe and that solution causes the orthopedic and the related liability problems discussed above.